1. Field of the Invention
This invention relates to a method of producing deep bore holes, particularly in wood and similarly structured materials, a deep boring drill suitable for this purpose and a deep boring drill apparatus used for executing the method.
2. Description of Prior Art
In the course of working materials, it is at times necessary to drill deep holes in a workpiece. In so doing, special attention must be paid to ensure that the drill does not run off center in the drill hole and, as a result, miss the desired direction. When working wood, the danger of the drill running off center is greatly increased due to the structure formed by the annual rings.
The removal of the chips must also be given careful consideration. With a long conveying path, in particular, the chips can block the drill, causing the drill to break. This, too, is the case, particularly in woodworking, due to chips frequently breaking off in large pieces.
In woodworking, the drilling of deep holes is mostly circumvented by either slitting a workpiece or machining a groove, and subsequently closing the open surface. The resulting seam is sometimes undesirable, particularly if it is located in plain view.
Different deep boring drills and methods connected therewith are known in the art which solve the problem of off-center running or chip removal in different ways. However, these deep boring drills are mainly employed for working metal or ceramics.
The deep boring drill disclosed in Swiss Patent Publication CH-A-653 270 operates by intermittent retraction, wherein the drill is automatically removed at constant time intervals, thereby removing the chips. Conventional twist drills are employed as drills.
However, this method has some disadvantages. For one, it requires an elaborate control for optimizing the advance and retraction moves in time for preventing the drill from reaching the end of the drill hole at too great a speed. Secondly, the drilling process is interrupted several times, not only resulting in loss of time, but also reducing the evenness of the drill hole. Thirdly, not all the chipped-off material is removed. The deeper the drill hole becomes, the greater the remainder of chips left in the drill hole becomes, which can result in blockage of the drill.
A deep boring drill is taught by British Patent Disclosure GB-A-1,415,137, the cutting elements of which are located in a tube. A second tube is centered in the first tube and connected to it, fixed against relative rotation. It is used for supplying a coolant which subsequently flows back out of the drilling location through the annular chamber between the two tubes. In so doing, it also removes the chips generated by the drilling. The construction of this drill is suitable only in a limited way for woodworking. If large chips break off, they can block the annular chamber and block the removal of chips. This possibly is further increased by the fact that the two concentric tubes are immovable with respect to each other.
A rotating circular saw device is taught by German. Patent Publication DE-A-26 24 371, having a guide drill and a rotating circular saw. The guide drill is a twist drill, on which the rotating circular saw in the form of a crown drill is fastened, fixed against relative rotation. In addition, the guide drill is seated ahead of the rotating circular saw. This device is not suitable for woodworking. If the guide drill moves along an annual ring, this can lead to off-center running of the drill.
Consequently, all known systems operate with one or more drill heads which can in part have different cutting surfaces, but which are connected to each other, fixed against relative rotation and, consequently, always operate at identical rpm.